It is reported in, for example, JP-A-5-265212 that resists produced by using a 2-alkyl-2-adamantyl ester as a raw material shows high resistance to dry etching in a process for production of semiconductor. Therefore, attention is being paid to a future prospect of 2-alkyl-2-adamantyl ester as a raw material for semiconductor resist.
For production of 2-alkyl-2-adamantyl ester, there are known, for example, a process which comprises subjecting 2-adamantanone to alkylation using an alkylation reagent composed of an organometallic compound and then subjecting the resulting metal salt of 2-alkyl-2-adamantanol to acylation using a carboxylic acid halide compound. Specifically, it is described in JP-A-10-182552 that 2-methyl-2-adamantyl methacrylate is obtained at a yield of 85.0% by using 2-adamantanone, methyl magnesium bromide and methacrylic chloride.
In such a production process, conditions are known in which an alkylation reaction of 2-admantanone using methyl magnesium bromide proceeds stoichiometrically. Therefore, the yield of the latter step, i.e. the acylation reaction of magnesium halide salt of adamantanol has an influence on the yield and purity of intended product, i.e. 2-alkyl-2-adamantyl ester.
The present inventors traced the acylation reaction described in the above literature; however, the reaction was not complete even when the reaction was made at room temperature for 15 hours, the conversion was 86%, and the purity of the intended product obtained was 77%.
When the 2-alkyl-2-adamantyl ester is used as a raw material for semiconductor resist, the ester is required to have a high purity. In the conventional production process therefor, however, the conversion in acylation is low as mentioned above and complicated purification is necessary, making it impossible to produce a 2-alkyl-2-adamantyl ester of high purity efficiently.
Further, the carboxylic acid halide compound used in the production process is ordinarily produced from a carboxylic acid compound and therefore is more expensive than the carboxylic acid compound. Furthermore, the carboxylic acid halide compound is highly reactive per se and therefore may require care in handling.
Incidentally, as a general process for production of an ester compound, there is a process which comprises reacting an alcohol compound with a carboxylic acid compound in the presence of an acid catalyst. In this process, the reaction is conducted with removing the water as by-product by azeotropic dehydration (for example, Azeotropic Dehydration, Organic Synthesis 1973, Vol. V, p. 762).
The process is conducted by a simple operation and therefore is particularly useful as an industrial process for production of ester compound when the alcohol compound and carboxylic acid compound used are inexpensive.
In this process, however, dehydration reaction of alcohol takes place preferentially as shown in Comparative Example 7 described later, when a tertiary alcohol such as 2-alkyl-2-adamantanol is used as a raw material. As a result, the process has a problem in that the yield of alkyladamantyl ester is strikingly low.